There are 1.1 million persons living with HIV (PLWH) in the US: 60% smoke cigarettes and 75% are interested in quitting. Two-thirds of PLWH use the Internet, making this a promising avenue to deliver smoking cessation treatment. Almost none are currently accessing smoking cessation interventions designed to meet their specific needs and concerns. Cigarette smoking is responsible for 24%--61% of deaths among PLWH, and 30% of non-AIDS defining malignancies. It is driving the alarming rise in lung cancers in this highly vulnerable population. The lack of access to proven, effective, culturally appropriate tobacco cessation services represents a health disparity of the first order. Cessation websites offer smokers convenience, low (or no) cost, and anonymity; however, there are no publicly available web-based cessation programs specifically designed for PLWH smokers. Smokers living with HIV have high rates of nicotine dependence, anxiety, depression, loneliness, and substance use. We developed Positively Smoke Free on the Web (PSFW), a theory-driven, culturally tailored web-based program designed to address the specific needs of PLWH smokers. Our NCI-funded R21 pilot of PSFW demonstrated moderate-high levels of adherence and yielded higher 3-month abstinence rates compared to standard care (10% vs. 4%). Our prior research on web-based cessation interventions has shown that smokers who participate in an online community - whether passively reading posts by others or actively engaging in online discussions - are more than twice as likely to achieve abstinence even after controlling for a broad range of covariates. In preparation for the proposed study, our partners at the American Legacy Foundation have enhanced and modernized PSFW by integrating an online community platform (now PSFW+), developing a training protocol for PLWH smoker seed users (to provide a critical mass of social network participants), and recruiting and training 11 PLWH smokers for this role. The prototype PSFW+ application has been successfully alpha- and beta-tested in anticipation of the randomized controlled trial. We propose a study that will compare the efficacy of the PSFW+ smoking cessation website to an attention- matched website promoting cardiovascular health in a randomized controlled trial with repeated measures at baseline, 1, 3, and 6 months. Participants will be N=550 PLWH smokers interested in quitting in the next 30 days. All participants will be offered nicotine replacement therapy. It is hypothesized that PSFW+ will outperform the control condition on the primary outcome of 7-day point prevalence abstinence at 6 months post-randomization. Secondary aims and exploratory analyses will examine theory-driven hypotheses about the mediators and moderators of treatment outcome (e.g., depression, anxiety, social support, loneliness, self-efficacy). Establishing the effectiveness of a web-based smoking cessation program for PLWH that has broad reach and could be scaled to reach PLWH smokers throughout the US would not only represent an enormous advance in the fight against tobacco use in PLWH, but would also provide a clearer understanding of the role of targeted, web-based health interventions in comprehensive HIV care.